"We do not know the number of customers affected at this time," company spokeswoman Stephanie Sheppard was quoted as saying by Reuters.

Hyatt said it identified unauthorised access to data on cards used at certain Hyatt-managed locations, primarily its restaurants.

The company also said the "at-risk window" for a limited number of locations began on or shortly after July 30.

The malware was designed to collect data such as cardholder name, card number, expiration date and internal verification code, the company said.

Hyatt said it has notified the appropriate country and state regulators and is working with the US Federal Bureau of Investigation.

Hyatt said it has arranged an identity protection and fraud detection firm to provide one year of free services to affected customers and has set up a Q&A page on its website to help customers who may be affected.

The company disclosed in December that its payment processing system was infected with malware but did not mention how long its network was infected.

Hyatt, controlled by the billionaire Pritzker family, is the fourth major hotel operator to warn of a breach since October.